FIG. 6 is a block diagram showing a connection between the personal computer 1007 and the conventional detector 1001. The personal computer 1007 comprises the root hub 1005 and the plug 1004. The root hub 1005 is a host for communication using the USB. The root hub 1005 and the plug 1004 are connected through the power line VBUS and the resistance R2. Electric potential VBUS is supplied to the peripheral device from the personal computer through a power line.
The detector 1001 comprises the level conversion and protection circuit 1002, MCU 1003, plug 1009, and the resistance R1. The MCU 1003 and the plug 1009 are connected through the USB communication line transmitting electrical potential for a differential signal of a D+ voltage level, and the USB communication line transmitting electrical potential for a differential signal of a D− voltage level. The resistance R1 is connected between the MPU 1003 and the USB communication line transmitting D− electrical potential. The resistance R1 transmits an output VREG of a regulator built in the MCU 1003. The plug 1004 of the personal computer 1007 and the plug 1009 of the detector 1001 are connected through the cable 1006. Potential VBUS from the personal computer 1007 is applied to the level conversion and protection circuit 1002 through the plugs 1004 and 1009. When the potential VBUS is received, the level conversion and protection circuit 1002 outputs the VBUS detection signal to the MCU 1003.
In the conventional detector 1001 the level conversion and protection circuit 1002 is provided outside the MCU 1003. Thus, reception of potential VBUS is detected in this level conversion and protection circuit 1002 that is an external circuit with respect to the MPU 1003. The MCU 1003 detects connection of the detector 1001 and the personal computer 1007 based on the VBUS detection signal output by the level conversion and protection circuit 1002. Thus, in the conventional detector 1001 the level conversion and protection circuit 1002 is required and therefore it is difficult to reduce the size of the circuit.
Some times the detector is provided with a built in battery power supply and this battery is charged using the potential received from the personal computer. However, in such a detector it is difficult to perform fine detection of the connection, therefore, more circuitry is required to be provided. Therefore, there is a problem that it is difficult to reduce the size of the circuit.